1. Field of the Invention
The present invention relates to a light-sensitive lithographic printing plate. More particularly, the present invention is concerned with a light-sensitive lithographic printing plate which is improved in ease of development in which a light-sensitive layer is subjected to imagewise exposure and then soluble areas of the light-sensitive layer are removed with a solvent (hereinafter referred to as developability), and in more preferred embodiments, which is developable with an alkaline aqueous solution without using any organic solvent.
2. Description of the Prior Art
Hydrophilic areas and oleophilic areas are formed on the surface of a lithographic printing plate, the hydrophilic areas being non-image areas and the oleophilic areas being image areas. In printing, the hydrophilic areas are first moistened with water to make them ink-repellent, the oleophilic areas are then inked, and the ink on the printing surface is transferred through offset rollers (blankets) to a receiving surface. Hitherto, light-sensitive materials have been used in producing light-sensitive layers photographically, producing the hydrophilic areas and the oleophilic areas according to the printing images desired on the lithographic printing plate. As light-sensitive materials for use in a negative type plate wherein exposed areas of the light-sensitive layer are made oleophilic and unexposed areas of the light-sensitive layer are made hydrophilic or removed by a solvent (in this case, upon removal of the areas the hydrophilic layer previously provided under the light-sensitive layer is exposed). Examples of such materials include a condensate of p-diazophenylamine and formaldehyde as described in West German Pat. No. 596,731, and derivatives thereof; 3-nitroanthranyl acid as described in U.S. Pat. No. 2,729,562; diazo derivatives of aromatic or heterocyclic amines as described in West German Pat. No. 949,383; reaction products of polysulfonic acid salts and diazonium salts as described in U.S. Pat. No. 2,890,115; an acrylic acid ester of pentaerythritol as described in Japanese Patent Publication No. 32714/1971; polyvinylcinnamic acid as described in U.S. Pat. No. 3,357,831; etc.
Recently, various materials exhibiting phenomena such as photo-crosslinking, photo-polymerization, etc., have been developed, and some of these materials are now in practical use. Of these materials, light-sensitive materials exhibiting photo-crosslinking are those polymers whose light-sensitivity is provided by introducing --CH.dbd.CHCO-- units into the main chain of a polymer such as a polyester, polycarbonate, polysulfonate, etc., at the time of producing these polymers. While light-sensitive lithographic printing plates produced using these light-sensitive polymers are highly sensitive and have a sharp sensitivity curve (high .gamma.), they suffer from the defect that developability is poor. Therefore, while one might consider removing this defect by blending these polymers with other polymers, the compatibility of these polymers with other polymers is extremely poor and polymers which are mutually soluble with these light-sensitive polymers are very limited. Though there are some other polymers mutually soluble with these light-sensitive polymers, the compositions produced by blending them do not exhibit highly improved properties.